The present invention relates to controlling the dusting of coal. More particularly, it relates to an improved process for treating coal with a dust suppressing liquid.
The problems of coal dusting are well known, for example, as described in the article by W. H. Miller, "Coal Dust Control", Coal Technology 1980 Volume 3, 3rd International Coal Utilization Exhibition and Conference, Houston, Texas, 1980, pages 285-320. As far as Applicants are aware, the prior treatments with dust suppressing liquids have been limited to uses of water, water containing a surfactant, oils or waxes, or the like.
Release of fugitive dust from coal, i.e., particles less than about 100 micrometers in size, is a major problem. This problem is encountered throughout the coal handling industry--at the mine, at transfer points, and at utilities or other points of utilization. The problem may be compounded due to the close proximity of transfer points and utilities to populated or environmentally sensitive areas.
Commercially available dust suppression systems include devices which capture entrained dust, induce the dust to settle, or contain the dust. However, the most common method is to wet the coal with water to prevent dusting. Water is inexpensive and large quantities can be added to eliminate dust. But, adding water decreases the specific heating value of the coal. This increases the total weight that must be moved and handled from the treating point and hence increases handling and transportation costs. However, the flow properties of water-wetted coal also may be adversely affected. In addition, the decrease in the specific heating value of the coal may require derating of a utility's power plant due to weight limited devices such as pulverizers.
Water or surfactant-doped water provides a bridge or binder between the dust particles. This bridge is not extremely strong and is volatile. Thus, the bridge can be eliminated by evaporation, and this in turn requires further water addition. When dried coal with no surface moisture is handled, there is no water to agglomerate the dust particles. Consequently, untreated dried coal is dusty and may require more water to suppress dust. This could potentially offset the effect of drying. But, since volatile water has been removed, a nonvolatile agent can be applied to agglomerate the dust.